1. Field of the Invention
The present invention relates to a novel polysaccharide derivative, and more particularly to a novel polysaccharide derivative which has excellent transparency when dissolved in water, exhibits excellent thickening ability at a low concentration, undergoes little change in viscosity of its aqueous solution even either in coexistence with metal salts or by temperature changes and moreover shows extremely good emulsion stabilizing ability, a preparation process thereof, use of the polysaccharide derivative for a thickener for cosmetic compositions, and cosmetic compositions containing the same.
2. Description of the Background Art
Various cellulose ethers are widely used as one of important ingredients of cosmetics, toiletries, medicines for external application, water-soluble paints and the like, and as a thickener, gelling agent, excipient, emulsion stabilizer and/or flocculant. As such cellulose ethers, water-soluble nonionic cellulose ethers such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose and ethylhydroxyethyl cellulose, ionic cellulose ethers such as carboxymethyl cellulose, cationized cellulose and cationized hydroxyethyl cellulose, and the like are commercially available and in use.
These cellulose ethers are relatively excellent in viscosity stabilizing ability for aqueous solutions in systems coexistent with inorganic metal salts or organic metal salts compared with polyacrylic acid type thickeners such as Carbopol, but are lower in thickening ability at the same concentration in an aqueous solution as the above thickeners. Therefore, it has been necessary to increase the amount of the cellulose ethers to be used to sufficiently exhibit their properties when used as a thickener or emulsion stabilizer for, in particular, cosmetics, toiletries and the like. However, the incorporation of the cellulose ethers in a great amount has caused problems from the viewpoint of feel such as a sticky feel and a filmy feel and has been accompanied by a drawback that the resulting product undergoes a great change by temperature changes and is hence difficult to be maintained in a stable form.
On the other hand, for example, Japanese Patent Application Laid-Open Nos. 110103/1980 and 801/1981 disclose that a hydrophobized nonionic cellulose derivative obtained by partially introducing a long-chain alkyl group having 10-24 carbon atoms into a nonionic water-soluble cellulose ether exhibits comparatively high thickening ability when mixed in a small amount with water. As found in Japanese Patent Application Laid-Open Nos. 12401/1991, 141210/1991, 141214/1991 and 218316/1991, an attempt has also been made to apply these alkyl-substituted cellulose derivatives to medicines for external application, cosmetic compositions and the like. However, these alkyl-substituted cellulose derivatives have excellent thickening ability compared with the cellulose ethers, but are poor in water solubility, and have hence involved such problems that it takes a long period of time to be evenly dissolved upon incorporation into a product, and they are poor in viscosity stability with time.
An ideal thickener to be used in cosmetics and toiletries requires that it is easily dissolved to exhibit an excellent thickening effect, the viscosity of its solution is scarcely affected by metal salts, surfactants, oily substances and other additives coexistent therewith, changes in temperature and pH, such a solution scarcely undergoes a change in viscosity with time, and it gives users a pleasant feeling upon use without being sticky to the touch and has excellent microbial resistance. However, the cellulose ethers and alkyl-substituted cellulose derivatives have not fully satisfied all of these performance characteristics required.